Right, a suggestion I made here in another topic made me wonder why not try that myself. A bunch of data was sitting on the PDS, after all. After a hassle figuring out just how the image cubes are organized and trying to read them, finally I was able to produce some results. This is all very rough work, can be considered first-iteration only and not particularly accurate. Basically, I used the cubes to extract the visible spectrum in the 380-780 nanometer range which was then input to color matching code I found here by Andrew T. Young.The code integrates over 40 10-nm steps to produce CIE XYZ color components. I then converted these to RGB values.

I'm aware of at least three inaccuracies in my code as of yet: one is the above sampled code apparently uses Illuminant C as the light source, not true solar spectra so the color turns out bluish (has a temp. of 9300 K instead of 6500 K, AFAIK). I tried to compensate at the moment by changing the final RGB white balance, but this is probably an inaccurate way to go. Another inaccuracy is I don't do bias removal from the cubes. This likely affects the outcome. Also, I don't use the precise wavelengths the code requires, but use the closest one in the cube. I intend to fix this by interpolating between nearest wavelengths.

All images are enlarged 4x.

The leftmost image is a 4-cube mosaic. The colors in all four frames turned out identical which gives me at least some confidence. The image in the middle shows Dione's disc creeping in front of Saturn. Dione's disc appears elongated probably because as the lines were readout, it moved considerably in its orbit. The rightmost image shows a very overexposed Saturn image, the part below the ring shadows got overexposed. From what I've seen browsing through the PDS, a lot of the cubes are badly overexposed at some wavelengths.

Here's a couple of Jupiter images. I'm not very satisfied with them as they seem to look somewhat greenish, but overall the color looks believeable:

Lastly, two Titan composites. They turned out way more reddish than I thought they would.

It'll be interesting to see how much the results will change once I do a more proper processing pipeline working.

Part of my confusion on this might be coming from a misunderstanding about what the dataset is providing. Are the VIMS cubes in spectral power, or reflectance? (I appologize if I'm using these terms incorrectly) Has the illuminant spectrum already been removed?

If the VIMS data is in spectral power, then I would say that chromatic adaptation is still necessary since, as Don said, D65 isn't solar spectrum. It is what we see here on Earth.

If it is a reflectance dataset, then wouldn't that spectrum have to be multiplied by the spectrum of the D65 illuminant before being passed to the CIE color matching functions?

If the VIMS data is in spectral power, then I would say that chromatic adaptation is still necessary since, as Don said, D65 isn't solar spectrum. It is what we see here on Earth.

If it is a reflectance dataset, then wouldn't that spectrum have to be multiplied by the spectrum of the D65 illuminant before being passed to the CIE color matching functions?

It's worse than that.

In most of these cases, monitors are inherently dimmer than the sunlit surfaces we're talking about, and the relative sensory-system response to the three primary colors can and does shift as you increase/decrease illumination. So let's say some body out there simply reflected twice the green light it did blue light, reflecting those only in narrow bands, and it reflected no red at all. It would not necessarily capture the color of that object merely to have a display also emit twice the green light as blue; if the illumination is different, then a different ratio must be used to capture the ratio of color responses one would have seeing that object in daylight. An extreme example of this can cause the apparent relative brightness of two patches to depend on the illumination in which you view them -- even if the light sources both have solar spectrum! Another related phenomenon is that it is often possible to see sun dogs or dim rainbows if you are wearing sunglasses, only to have the color disappear when you take the sunglasses off.

I computed once that Uranus (and bodies beyond that, for the most part) has a luminance that a computer monitor can match, but everything closer to the Sun than that is brighter than your monitor could display. So achieving the colors one would perceive from a spaceship window requires some trickiness.

I computed once that Uranus (and bodies beyond that, for the most part) has a luminance that a computer monitor can match, but everything closer to the Sun than that is brighter than your monitor could display.

Now that would be something... getting a totally dark room around you with an image of Neptune on the screen that is precisely as bright as the real thing and your eye is accustomed to the low light. I wonder how dim that'd appear. It would be difficult to calibrate, though. I imagine you'd need one of those Light Intensity Measuring Thingies (LIMTs).

There are CRT monitors nowadays that have a sort of "Magic Bright" function that kicks up the brightness substantially, I imagine accurate luminances could be reached even at Saturn, though I'm not so sure about Enceladus and Tethys, them being so high-albedo and all.

I can understand the reasoning of not touching the illumination, not removing solar spectra from the cubes. The problem with that is solar spectrum turns out reddish and everything has a distinct red hue. Here are a couple of comparisons, left images show no spectrum messing, simple integration through the CIE XYZ functions.

I suppose if you stared long enough at scenes like this, the eye/brain would automatically adapt to the color and make a new white-point, making Enceladus (uppermost left image) appear white again. The problem is, this is not gonna happen on a computer screen.

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